The present invention relates to a liquid discharge apparatus and liquid discharge method for determining a liquid discharge deflection amount in accordance with the distance between a head's liquid discharge surface and a surface on which a discharged liquid is to land, and deflecting and discharging a liquid in accordance with the determined liquid discharge deflection amount.
A known example of a liquid discharge apparatus having a head in which a plurality of nozzle-incorporated liquid discharge sections are arranged is an inkjet printer. A thermal method is known as an ink discharge method for inkjet printers. The thermal method is used to discharge ink by making use of thermal energy.
A known structure employed for an ink discharge section based on the thermal method includes an ink liquid chamber, a thermal resistor provided in the ink liquid chamber, and a nozzle mounted on the ink liquid chamber. Ink in the ink liquid chamber is rapidly heated by the thermal resistor to form bubbles in the ink on the thermal resistor. Energy generated upon bubble formation discharges the ink (ink droplets) from the nozzle in the ink discharge section.
From the viewpoint of a head structure, two ink discharge methods are defined: serial method and line method. The serial method is used to make a print while moving the head in the direction of the width of print paper. The line method is used while many heads are arranged in the direction of the width of print paper to form a line head that covers the whole print paper width.
In a known line head structure disclosed a plurality of small head chips are positioned end to end so that liquid discharge sections of the head chips are arrayed to cover the whole print paper width. (for instance, by Japanese Patent Laid-open No. 2002-36522). A known technology disclosed, provides a printer head structure in which a plurality of heaters are variously positioned within an ink liquid chamber corresponding to one nozzle so as to vary the angle of ink droplet discharge. This ensures that diversified ink landing positions are rendered inconspicuous. (for instance, by Japanese Patent Laid-open No. 2002-240287). However, the above conventional technologies have problems that are described below.
When the ink is to be discharged from a head, it is ideal that the ink be discharged perpendicularly to the discharge surface. Due to various causes, however, the ink may not always be discharged perpendicularly to the discharge surface.
When, for instance, a nozzle sheet on which a nozzle is formed is to be attached to the upper surface of the ink liquid chamber having a thermal resistor, the correct positional relationship among the ink liquid chamber, thermal resistor, and nozzle needs to be observed. When the nozzle sheet is attached so that the nozzle center is in alignment with the center of the ink liquid chamber and thermal resistor, the ink will be discharged perpendicularly to the discharge surface. However, if the nozzle center is not in alignment with the center of the ink liquid chamber and thermal resistor, the ink will not be discharged perpendicularly to the discharge surface.
Positional displacement may also occur due to a thermal expansion coefficient difference among the ink liquid chamber, thermal resistor, and nozzle sheet.
When discharged perpendicularly to the discharge surface, the ink lands at a correct position. However, if the ink is not discharged perpendicularly to the discharge surface, the resulting ink landing position is displaced. If the ink landing position is displaced during the use of the serial method, ink landing pitch displacement occurs between nozzles. If, on the other hand, the ink landing position is displaced during the use of the line method, ink landing position displacement occurs between arrayed heads in addition to the above-mentioned ink landing pitch displacement.
More specifically, if the ink landing positions provided by adjacent heads are displaced away from each other, the ink is not discharged to a certain area between the heads. Further, the line head does not move in the direction of the width of print paper. Therefore, a white streak appears between the heads to the detriment of print quality.
On the other hand, if the ink landing positions provided by adjacent heads are displaced toward each other, dots overlap in a certain area between the heads. Consequently, a discontinuous print image or an unduly dark streak may result to the detriment of print quality.
Technologies are therefore proposed by the applicant of the present invention to solve the above problems (e.g., Japanese Patent Application No. 2002-112947 and Japanese Patent Application No. 2002-161928). These technologies utilize a technology disclosed by Japanese Patent Laid-open No. 2002-240287, which is mentioned above, and make it possible to control (deflect) the liquid discharge direction in a liquid discharge apparatus that has a head in which a plurality of liquid discharge sections are arrayed.
However, if the same deflection angle is employed for the ink discharge direction in a situation where the print paper thickness varies or the distance (gap) between the ink discharge surface and ink landing surface of print paper varies, the above technologies do not cause the ink to land at precise positions.
FIGS. 17A and 17B illustrate prints that are made on print papers P1 and P2, which differ in paper thickness, with the ink discharge angle deflected by α FIG. 17A indicates that a print is made on print paper P1 with the ink discharge angle deflected by α when the distance between the ink discharge surface (the end face of head 1) and the ink landing surface of print paper P1 is L1.
When head 1, which has the above characteristics, is used with print paper P2, which differs from print paper P1 in paper thickness (print paper P2 is thicker than print paper P1), the distance between the ink discharge surface and the ink landing surface of print paper P2 changes from L1 to L2 (L2<L1). If the ink discharge angle is similarly deflected by α in the resulting state, the ink landing positions differ from those prevailing when print paper P1 is used.
In some cases, the surface height of a single sheet of print paper may partly vary if, for instance, an envelope having a fold or label print paper is used. Further, if a printed circuit board containing a circuit pattern is used, the surface height considerably varies. Furthermore, if the employed print paper has a curled edge, the surface height of such a curled edge differs from that of the other portion.
In the above cases, print paper and other similar materials having varying surface heights cannot be properly printed even if the ink discharge angle is properly adjusted prior to printing.